高岭背靠背直流系统过流保护动作案例分析

Case Study on Over-current Protection Action of Gaoling Back-to-back HVDC System

换相失败是高压直流输电系统最常见的故障之一,它可导致直流电压降低、直流电流增大、直流输送功率减少、换流阀寿命缩短、换流变压器直流偏磁及逆变侧弱交流系统过电压等不良后果,严重工况时可能引发直流闭锁等严重故障。介绍了高岭背靠背直流单元Ⅰ发生的因交流系统扰动而产生的一次闭锁事件,交流系统故障使得直流系统换相失败,导致直流过流保护动作而闭锁。在介绍事件发展经过的基础上,结合高岭直流历次换相失败产生过程,讨论了直流过流保护动作的原理。最后,从直流系统保护配置、交流系统稳定水平、直流控制保护系统、电网运行人员素质等4个方面给出了提升交、直流系统安全稳定运行水平的相关建议与改进措施。

Commutation failure is one of the most common faults in the high-voltage direct current（HVDC）transmission system,which can lead to results such as ： DC voltage reducing,DC current increasing,DC transmission power reducing,shorter life span of the converter valves,converter transformer DC magnetic bias and over-voltage of weak AC system on inverter-side.And in severe conditions,it may result in DC block fault and other serious problems.A DC block event occurred in the Gaoling back-to-back DC unitⅠcaused by AC system disturbance is described.AC system failure made DC system to produce commutation failure and to result in DC over-current protection action and unitⅠ block fault.Based on detailed event process,the principle of DC over-current protection action is discussed in detail,combining of Gaoling back-to-back DC system previous commutation failures.Finally,the recommendations and improvements about enhancing the security and stability level of AC and DC systems are given from four aspects such as ： the DC system protection configuration,AC system stabilization level,DC control and protection system,and quality of power grid operating personnel.